High Elongation Electroless Copper Process

ABSTRACT

An electroless copper deposition composition, comprising: (a) a source of copper ions; (b) a chelator; (c) a source of alkalinity; (d) a reducing agent; (e) nickel ions; (f) a bipyridine; (g) optionally, an additional stabilizer; and (h) optionally, a water soluble polymer. The electroless copper deposition composition can be used to deposit a ductile copper deposit on a substrate that exhibits high % elongation and high tensile strength.

FIELD OF THE INVENTION

The present invention relates generally to electroless copper platingsolutions capable of producing ductile copper deposits and methods forproducing ductile copper plating deposits by electroless copper plating.

BACKGROUND OF THE INVENTION

Electroless copper plating baths are widely used in metallizationindustries for depositing copper on various types of substrates. Forexample, in the manufacture of printed circuit boards, electrolesscopper baths are used to deposit copper on walls of through-holes andcircuit paths as a base for subsequent electrolytic copper plating.Electroless copper plating is also used in the decorative plasticsindustry to deposit copper on non-conductive surfaces as a base forfurther plating of copper, nickel, gold, silver and other metals.

Commercial electroless copper baths generally contain water-solubledivalent copper compounds, chelating agents or complexing agents,reducing agents, and various other additives to make the bath morestable, adjust the plating rate and brighten the copper deposit.

In electronics manufacturing, electroless copper plating solutions canbe used to deposit copper on printed circuit boards, chip carriers andsemiconductor wafers as well as any other circuit carriers andinterconnect devices. The copper plating solutions can be used inprinted circuit boards and chip carriers, and also for semiconductorwafers, to plate surfaces, trenches, blind micro vias, through hole vias(through holes) and similar structures with copper, and can be used todeposit of copper on surfaces, in trenches, blind-micro-vias,through-hole-vias, and comparable structures in printed circuit boards,chips, carriers, wafers and various other interconnect devices. The term“through hole vias” or “through holes”, as used in the presentinvention, encompasses all kinds of through hole vias and includesso-called “through silicon vias” in silicon wafers.

Electroless copper deposits plated over the walls of through-holes,vias, interconnects, etc. provides conductivity between surfaces of aboard and/or between circuit layers. In additive circuit manufacture, inaddition to providing conductivity between surfaces and/or circuitlayers, the deposit also serves as the conductor lines.

With increased circuit density, and with more rigorous specificationsfor circuit boards, the mechanical properties of a deposit becomeincreasingly important, especially deposit ductility. For example, inthe manufacture of electronic devices, it is necessary to soldercomponents to a circuit board. The solder increases the temperature ofthe electroless deposit which causes it to expand and then contract withcooling. The coefficient of expansion of the copper differs from thecoefficient of expansion of the surface over which the copper is plated.Therefore, stress is created in the copper which can cause cracking ofthe deposit, which can result in failure of the circuit board.

Electroless copper is significantly less ductile than other forms ofcopper (i.e. such electrolytically deposited copper). For example,electroless copper deposits typically possess an elongations of about0.5 to 3.5 percent while electrolytic copper, as used in the manufactureof through-hole printed circuit boards, typically possesses an elongatein the range of from about 6 to 15 percent. Thus, there remains a needint the art for improved electroless copper plating solutions that canproduce a more ductile deposit for use in the manufacture of printedcircuit boards and other similar substrates.

In practice, current electroless copper solutions have only been capableof achieving an elongation percentage of about 2-3%, and no electrolesscopper systems (MID) electroless copper systems currently on the markethas been able to offer high elongation. Thus, there remains a need inthe art for an improved copper electroless plating bath and platingmethod that can achieve high % elongation and sufficient tensilestrength.

While there are commercial electroless copper baths that contains Niions, these baths typically also contain CN derivatives or EDTA, bothwhich causes the Ni ion benefit to be minor, and that also require ahigh concentration of nickel metal ions (i.e., about 700-1000 ppm ormore).

For example, U.S. Pat. No. 4,695,505 to Dutkewych, the subject matter ofwhich is herein incorporated by reference in its entirety, describes anelectroless copper deposit having an elongation capability of at least10% by including a minor amount of a source of nickel ions and cyanideand/or ferrocyanide in the plating solution. Dutkewych suggests thatwith an adequate concentration of cyanide ions, an increase inelongation capability is realized when the nickel content is as low asabout 5 ppm. However, Dutkewych requires that the composition containcyanide ions in order to achieve the desired result which is notdesirable from an environmental standpoint.

Thus, there remains a need in the art for an improved electroless copperelectroplating solution that can provide a ductile copper depositexhibiting a % elongation of at least about 10%. In addition, thereremain a need in the art for an improved copper electroplating solutionthat can provide a ductile copper deposit and that has both a cost andenvironmental benefit.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improvedelectroless copper plating solution.

It is another object of the present invention to provide an electrolesscopper plating solution that is capable of providing a ductile copperdeposit on an underlying substrate.

It is still another object of the present invention to provide a ductilecopper deposit that exhibits high elongation and high tensile strength.

It is still another object of the present invention to provide anelectroless copper plating solution that is at least substantially freeof cyanide and/or cyanide derivates and that is also at leastsubstantially free of ethylenediaminetetraacetic acid (EDTA).

It is still another object of the present invention to provide anelectroless copper plating solution that is at least substantially freeof any amino acids.

It is still another object of the present invention to provide anelectroless copper plating solution that includes only a minor amount ofnickel in the plating solution.

To that end, in one embodiment, the present invention relates generallyto an electroless copper plating solution comprising:

A) a source of copper ions;

B) a chelator;

C) a source of alkalinity;

D) a reducing agent;

E) nickel ions;

F) a bipyridine;

G) optionally, but preferably an additional stabilizer; and

H) optionally, a water soluble polymer.

In addition, the present invention also relates generally to a method ofproducing a ductile copper deposit on a substrate using the electrolesscopper plating solution described herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The inventors of the present invention have discovered an improvedelectroless copper electroless plating solution that can produce aductile deposit on an underlying substrate. In one embodiment, theelectroless copper deposit exhibits high elongation and high tensilestrength. The electroless copper plating solution described herein isable to produce a deposit exhibiting such high elongation and hightensile strength without the use of undesirable additives.

As used herein, “a,” “an,” and “the” refer to both singular and pluralreferents unless the context clearly dictates otherwise.

As used herein, the term “about” refers to a measurable value such as aparameter, an amount, a temporal duration, and the like and is meant toinclude variations of +/−15% or less, preferably variations of +/−10% orless, more preferably variations of +/−5% or less, even more preferablyvariations of +/−1% or less, and still more preferably variations of+/−0.1% or less of and from the particularly recited value, in so far assuch variations are appropriate to perform in the invention describedherein. Furthermore, it is also to be understood that the value to whichthe modifier “about” refers is itself specifically disclosed herein.

As used herein, spatially relative terms, such as “beneath”, “below”,“lower”, “above”, “upper” and the like, are used for ease of descriptionto describe one element or feature's relationship to another element(s)or feature(s) as illustrated in the figures. It is further understoodthat the terms “front” and “back” are not intended to be limiting andare intended to be interchangeable where appropriate.

As used herein, the terms “comprises” and/or “comprising,” specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

As used herein the term “substantially-free” or “essentially-free” ifnot otherwise defined herein for a particular element or compound meansthat a given element or compound is not detectable by ordinaryanalytical means that are well known to those skilled in the art ofmetal plating for bath analysis. Such methods typically include atomicabsorption spectrometry, titration, UV-Vis analysis, secondary ion massspectrometry, and other commonly available analytically methods.

All amounts are percent by weight, unless otherwise noted. All numericalranges are inclusive and combinable in any order except where it islogical that such numerical ranges are constrained to add up to 100%.

The terms “plating” and “deposit” or “deposition” are usedinterchangeably throughout this specification. The terms “composition”and “bath” are used interchangeably throughout this specification. Theterm “alkyl”, unless otherwise described in the specification as havingsubstituent groups, means an organic chemical group composed of onlycarbon and hydrogen and having a general formula: C_(n)H_(2n+1). Theterm “average” is equivalent to the mean value of a sample. All amountsare percent by weight, unless otherwise noted. All numerical ranges areinclusive and combinable in any order except where it is logical thatsuch numerical ranges are constrained to add up to 100%.

The present invention relates generally to an electroless copper coatingcomposition and a method of using the same to provide a copper depositexhibiting desired physical properties of high elongation and hightensile strength that are much improved over standard electroless coppercoatings currently in the market. The process is applicable in moldedinterconnect device (MID) applications where it is highly desirable thatstray plating does not occur and that there should be good adhesion tothe substrate. The electroless copper compositions described herein arealso applicable in other processes including, for example, standardcircuit board production and interconnect substrate production.

It is desirable that the copper deposit produced has an elongation ofgreater that about 10%, more preferably greater than about 12%, evenmore preferably greater than about 14%, and even more preferably,greater than about 15% with a tensile strength of greater than about30,000 psi, more preferably greater than about 40,000 psi, and even morepreferably greater than about 50,000 psi as measured using ASTM E-345.Under these conditions, adhesion to the MID substrate is capable ofpassing industry standard tape tests according to IPC-TM-650-IPC TestMethods. In addition, electroless copper plating deposits produced bythe methods described herein also exhibit minimal, and preferably nostray plating on MID substrates.

In one embodiment, the electroless copper composition comprises:

A) a source of copper ions;

B) a chelator;

C) a source of alkalinity;

D) a reducing agent;

E) nickel ions;

F) a bipyridine;

G) optionally, but preferably an additional stabilizer; and

H) optionally, a water soluble polymer.

The electroless copper composition described herein is an aqueoussolution, meaning that the primary solvent of the solution is water.Optionally, additional liquids that are miscible with water, includingalcohols and other polar organic liquids may also be added to thecomposition and would be usable in the compositions described herein.

The source of copper ions may be any suitable copper salt, includingcopper chloride, copper sulfate, copper nitrate, copper oxide, andcombinations of the foregoing. In one preferred embodiment, the sourceof copper ions is copper sulfate. In another preferred embodiment, thesource of copper ions is copper chloride. The concentration of the Cuion is generally in the range of about 0.1 to about 10 g/L, morepreferably about 0.5 to about 4 g/L, and even more preferably, in therange of about 2 to about 4 g/L.

Because simple copper salts are insoluble at a pH above about 4, achelating system is needed, and various chelators can be in theelectroless copper plating baths of the invention. Examples of chelatorsor chelating agents include tartaric acid and salts thereof, citric acidand salts thereof, malic acid and salts thereof, acetic acids and saltsthereof and other similar compounds. In one preferred embodiment, thechelator is a salt of tartaric acid, such as a salt of tartaric acidcontaining one or both of sodium and potassium. In one preferredembodiment, the tartaric acid salt comprises sodium potassium tartrate.However, while historically ethylenediaminetetraacetic acid (EDTA) hasbeen used as a chelator in electroless copper plating baths of thepresent invention, it is generally preferred that the electroless coppercomposition of the present invention be at least substantially free ofEDTA, more preferably that the bath does not contain EDTA in anymeasurable amount. That is, because of the very high affinity of EDTAfor any metal ions, even small residual amounts of EDTA can complex withmetal ions, making it more difficult to treat the resulting wastestream.

In one embodiment, the molar ratio of the complexing agents, related tothe total molar amount of all complexing agents, to copper ions is inthe range of 1:1 to 10:1, preferably 1:1 to 8:1, more preferably 1:1 toabout 4:1. A molar ratio of 1:1 to 4:1 of complexing agent(s) to copperions means about 1 to 4 equivalents of complexing agent(s) related tocopper.

The source of alkalinity may be any suitable source of alkalinity and isused in an amount sufficient to adjust the solution pH to between about11.0 and 14.0, more preferably between about 12.0 and about 13.0. In onepreferred embodiment, the source of alkalinity is a hydroxide, such assodium hydroxide or potassium hydroxide. The amount needed to achievethe desired pH may be within the range of about 1 to 15 g/L, morepreferably about 5 to about 10 g/L.

The reducing agent may be any suitable reducing agent that aids inreducing the copper ions in order to obtain metallic copper for plating.Reducing agents include, but are not limited to, aldehydes, such as,formaldehyde, formaldehyde precursors, formaldehyde derivatives, such asparaformaldehyde, borohydrides, such sodium borohydride, substitutedborohydrides, boranes, such as dimethylamine borane (DMAB), saccharides,such as grape sugar (glucose), glucose, sorbitol, cellulose, cane sugar,mannitol and gluconolactone, hypophosphite and salts thereof, such assodium hypophosphite, hydroquinone, catechol, resorcinol, quinol,pyrogallol, hydroxyquinol, phloroglucinol, guaiacol, gallic acid,glyoxylic acid, 3,4-dihydroxybenzoic acid, phenolsulfonic acid,cresolsulfonic acid, hydroquinonsulfonic acid, catecholsulfonic acid,tiron and salts of all of the foregoing reducing agents. Preferably, thereducing agents are chosen from formaldehyde, formaldehyde derivatives,formaldehyde precursors, borohydrides and hypophosphite and saltsthereof, hydroquinone, catechol, resorcinol, and gallic acid. Morepreferably, the reducing agents are chosen from formaldehyde,formaldehyde derivatives, formaldehyde precursors, and sodiumhypophosphite. Most preferably, the reducing agent is formaldehyde. Theconcentration of the reducing agent in the copper plating bath ispreferably within the range of about 1 g/L to about 15 g/L, morepreferably about 2 g/L to about 10 g/L, and even more preferably about 3g/L to about 8 g/L.

In addition, the electroless copper plating bath of the presentinvention should contain nickel metal ions in a sufficient amount to aidin increasing e the elongation of the copper deposit to above 10%elongation. Any source of nickel ions can be used in the practice of theinvention. However, in one preferred embodiment, the source of nickelions is nickel sulfate. The nickel ions are preferably present in theelectroless copper plating bath of the invention in an amount betweenabout 0.005 g/L to about 2 g/L nickel, more preferably between about0.01 g/L to about 1.0 g/L, even more preferably between about 0.02 andabout 0.04 g/L.

In the preferred embodiment of the present invention even 10-15 ppm ofNi ions is of great benefit to the physical properties and rate of thedeposit. However, this benefit at low nickel ion concentrations can onlybe realized if the solution is essentially free of EDTA and cyanide orcyanide derivatives. Lower Ni metal ion concentration has a desirablecost and environmental benefit.

The electroless copper plating baths described herein also include adipyridyl as a stabilizing agent. In a preferred embodiment, thedipyridyl comprises 2,2′-dipyridyl. The concentration of the dipyridylis typically within the range of about 0.001 g/L to about 0.05 g/L morepreferably about 0.002 to about 0.05 g/L, most preferably about 0.003 toabout 0.015 g/L.

In a particularly preferred embodiment, the electroless copper platingbath of the invention includes a combination of nickel metal ions and2,2′-dipyridyl, the combination of which has been found to produce anelectroless copper plating deposit that exhibits the desired ductility(% elongation) and tensile strength described herein.

In addition to the above bath constituents, the electroless copperplating solution may also comprise an additional stabilizing agent tofurther aid in stabilizing the plating solution against unwantedoutplating (i.e., unwanted and/or uncontrolled deposition of copper, forexample on the bottom of a reaction vessel or on other surfaces) in thebulk solution. This stabilizing function can be accomplished, forexample, by substances that act as catalyst poison (e.g., sulfur orother chalcogenide containing compounds) or by compounds formingcopper(I)-complexes, thus inhibiting the formation of copper(I)oxide.

Suitable stabilizers include any stabilizer that is free of CN groups.In one preferred embodiment, the stabilizer is an organic compoundcontaining divalent sulfur. Examples of suitable stabilizing agentsinclude, but are not limited to, dithiobiuret, diethyldithiocarbamate,ammonium (or sodium or potassium) pyrrolidinethiocarbamate, thiomalicacid, and other similar compounds. However, any cyanide-free stabilizingagent or mixtures thereof that are capable of preventing decompositionof the copper electroless plating bath would be known to those skilledin the art and are usable in the compositions described herein. Inaddition, the stabilizing agent is also beneficially selected so that itdoes not significantly impact (i.e., decrease) the % elongation of thedeposit. The concentration of the additional stabilizer is generallywithin the range of about 0.000005 g/L to about 0.01 g/L, morepreferably about 0.00001 to about 0.0001 g/L, most preferably about0.00002 g/L to about 0.00008 g/L.

In one preferred embodiment, the electroless copper plating bath alsocomprises a water-soluble polymer. Suitable water-soluble polymersinclude those having a molecular weight of at least 300 g/mol. While itis not required that the bath composition contain the polymer, in apreferred embodiment, the bath contains the water-soluble polymer. Onepreferred polymer that may be used in the bath of the invention ismethoxypolyethylene glycol. In a preferred embodiment, themethoxypolyethylene glycol has a molecular weight of at least 750 g/mol.This is preferred because it has a high enough molecular weight toincrease % elongation, but if higher molecular weightmethoxypolyethyleneglycol is utilized, the plating rate is slower whichis less desirable. The concentration of the water-soluble polymer isgenerally within the range of about 0.01 g/L to about 1 g/L, morepreferably about 0.05 to about 0.5 g/L, most preferably about 0.08 toabout 0.15 g/L.

Furthermore, it is also noted that polyethylene glycol (i.e., nomethoxy) is not desirable because it lowers the elongation of the copperdeposit. However, other polymers and surfactants that aid in increasingthe elongation (or that do not have a detrimental effect) can also beemployed. Other polymers include, for example:

1) Phosphate ester based surfactants, preferably moderate to low foamingvarieties;

2) Block copolymers of PEG/PPG such as “Pluronic” and “Tetronic”(available from Dow); and

3) Other polymers identified to increase the elongation of the copper.

In a preferred embodiment, the copper electroless solution should beessentially free of any cyanides, including NaCN, KCN, KFe(CN)₆, andK2Fe(CN)₆. The inventors have found that the presence of cyanide andcyanide derivatives in the bath can lower the elongation of theresulting deposit.

In addition, the electroless copper plating baths described herein alsodo not require an amino acid in the bath to produce the desired %elongation. That is, to be clear, in one preferred embodiment of theinvention, the electroless copper plating bath is free of any amino acidand contrary to certain prior art baths, the present invention does notrequire the presence of an amino acid to achieve the desired result.

The present invention also relates generally to an electroless copperplating bath consisting essentially of:

A) a source of copper ions;

B) a chelator;

C) a source of alkalinity;

D) a reducing agent;

E) nickel ions;

F) a bipyridine;

G) optionally, but preferably an additional stabilizer; and

H) optionally, a water soluble polymer.

By “consisting essentially of” what is meant is that the bath is free ofany additional components that would have a detrimental effect onductility, including % elongation and tensile strength.

In still another preferred embodiment, the present invention relatesgenerally to an electroless copper plating bath consisting of:

A) a source of copper ions;

B) a chelator;

C) a source of alkalinity;

D) a reducing agent;

E) nickel ions;

F) a bipyridine;

G) optionally, but preferably an additional stabilizer; and

H) optionally, a water soluble polymer.

In still another embodiment, the present invention relates generally toa method of electrolessly depositing copper on a substrate, the methodcomprising the steps of:

contacting the substrate with an electroless copper plating solution fora period of time to deposit copper on the substrate, the electrolesscopper plating solution comprising:

-   -   i) a source of copper ions;    -   ii) a chelator;    -   iii) a source of alkalinity;    -   iv) a reducing agent;    -   v) nickel ions;    -   vi) a bipyridine;    -   vii) optionally, but preferably an additional stabilizer; and    -   optionally, a water soluble polymer.

Once use of the bath begins, copper, caustic and formaldehyde areconsumed in the bath and must be replenished. This is routinely carriedout and the bath may be analyzed manually or automatically in order toreplenish the bath with a suitable replenishment chemistry.

For example, the substrate may be dipped or immersed in the solution ofthe invention. In the process a whole surface of a substrate may beplated with copper, or only selected portions.

The copper deposit produced in accordance with the present invention isable to obtain a % elongation of greater than about 10%, more preferablygreater than about 12%, even more preferably greater than about 13%, andeven greater than about 14%, and even greater than about 15%.

At the same time, the tensile strength of the deposit is greater thanabout 30,000 psi, more preferably greater than about 40,000 psi, mostpreferably greater than about 50,000 psi.

While not required, the process has a high plating rate at moderatetemperatures, the presence of the Ni ions in the plating bath describedherein (with no EDTA or CN or CN derivatives) increases the plating rateabove what is obtained in other baths with no Ni ions. The rateadvantage is especially apparent when comparing to other electrolesscopper baths that contain bipyridine. Normally bipyridine causes a lowerrate in these types of electroless copper baths and the higher thebipyridine concentration the lower the plating rate. However, in thebaths of the present invention, the use of bipyridine in the recitedconcentration range has virtually no effect on the plating rate. Inaddition, it was observed that the plating rate is higher than if the Niions were removed. So, the use of the Ni ions in the electroless copperplating bath of the instant invention provide two benefits (1) a higherplating rate, and (2) improved physical properties of the deposit. Theability to obtain a high plating rate at lower temperature allows thebath to be operated at lower temperatures which increases the stabilityof this and any electroless copper bath.

In one embodiment the solution is agitated during use, as would be knownto those skilled in the art.

The process is generally carried out for a sufficient time to yield adeposit of the desired thickness required, which depends on theparticular application.

In one embodiment, the substitute is a MID or a PCB. For example, theelectroless deposition of copper according to the process of theinvention can particularly be used for the through-plating of holes,surfaces, trenches, blind micro vias in printed circuit boards. Doublesided or multilayer boards (rigid or flexible) may also be plated bymeans of the present invention.

The process of the invention can be used to provide an electrolesscopper deposits with a thickness in the range of 0.05 to 10 μm dependingon the substitute.

Substrates used for printed circuit board manufacture are mostfrequently epoxy resins or epoxy glass composites. But other substances,notably phenolic resins, polytetrafluoroethylene (PTFE), polyimidespolyphenyleneoxides, BT (bismaleintriazine)-resins, cyanate esters andpolysulphones can be used. In addition, it is also contemplated that theprocess described herein can be used in a plating on plastics process toelectrolessly deposit copper on substrates such as ABS

In one embodiment, the electroless plating process is carried out at atemperature in the range of about 20 to about 60° C., more preferablyabout room temperature (i.e., about 25° C.) to about 55° C., even morepreferably about room temperature to about 45° C.

The plating rate is typically about 3 to 4 μm/hour at a temperature ofabout 40° C. Temperature and pH level can affect plating rate and can beadjusted if desired to adjust the plating rate.

In a preferred embodiment, it is beneficial and thus desirable tocontrol the plating rate while making the copper deposit at a constantrate. This can be accomplished, for example, by feeding the reactionchemicals with a chemical controller so that the deposition does notfluctuate (i.e., remains substantially constant) while the metal film isbeing deposited.

The substrate, i.e. the surfaces of the substrate that are to be platedwith copper, particularly non-metallic surfaces, may be pretreated tomake the substrates more receptive or autocatalytic for copperdeposition. In addition, all or only selected portions of a surface maybe pretreated. However, a pretreatment is not necessary in every caseand depends on the kind of substrate. Within the pretreatment step, itis also possible to sensitize substrates prior to the deposition ofelectroless copper on them. Which may be achieved by the adsorption of acatalyzing metal (i.e., a noble metal, such as palladium) onto thesurface of the substrate.

The pretreatment process depends various factors including thesubstrate, the desired application, and the desired properties of thecopper surface. In one embodiment, the substrate comprises ABS, whichhas been doped with a copper chromite catalyst. When this doped ABSmaterial is then ablated with a laser, the copper chromite catalystconcentrates on the surface and becomes active. Thus, plating onlyoccurs where the material has been ablated and isolated traces of metaldeposit onto the substrate. Therefore, no plating resist is required anda full-build electroless copper deposit directly forms the circuit whereit was ablated.

In another kind of pretreatment process a permanganate etching step isemployed, which is a multi-stage process, the steps of which are aswelling step, a permanganate etching step and a reduction step. Thesweller used in the swelling step is made of a mixture of organicsolvents. During this step drill smear and other impurities are removedfrom the surfaces of the substrate. A high temperature of 60-80° C.promotes the infiltration of the sweller which leads to a swelledsurface. Therefore, a stronger attack of the subsequently appliedpermanganate solution is possible during the permanganate etching step.Afterwards the reduction solution of the reduction step removes themanganese dioxides produced during the permanganate step from thesurfaces. The reduction solution contains a reducing agent andoptionally a conditioner.

The desmear process may be combined with the above described steps. Thedesmear process may be performed before step a) of the above describedpretreatment process or the desmear process may be performed instead ofsteps a) and b) of the above described pretreatment process.

The present invention will now be described with reference to thefollowing non-limiting examples:

In all of the examples below, the bath constituents are mixed togetherto form an aqueous electroless copper solution which is then used todeposit electroless copper on an ABS substrate by immersing the ABSsubstrate into the deposit for 270 minutes to provide an electrolesscopper deposit of about 13 μm on the substrates. The substrate is onethat is first doped with a copper chromite catalyst and laser ablated.Thereafter, % elongation and tensile strength are measured using ASTME-345 Standard Test Methods of Tension Testing of Metallic FoilIPC-TM-650 IPC Test Method.

In addition a tape test was performed according to industry standards byusing 3M® 600 tape, which is applied to the deposited copper film andthen peeled off rapidly at 90 degrees. An observation is then maderegarding whether the deposited copper film remains adhered to thesurface or is removed. If the metallic film remains adhered to thesurface, the metallic film is considered to pass the tape test.

The results are summarized in Table 1.

Example 1

Concentration Potassium sodium tartrate 0.08 M Copper (as sulfate orchloride) 0.03 M NaOH 8 g/L Formaldehyde 4 g/L Nickel Sulfate 0.025 g/L2,2′-dipyridyl 0.010 g/L

Example 2

Concentration Potassium sodium tartrate 0.10 M Copper (as sulfate orchloride) 0.04 M NaOH 10 g/L Formaldehyde 5 g/L Nickel Sulfate 0.050 g/L2,2′-dipyridyl 0.005 g/L

Example 3

Concentration Potassium sodium tartrate 0.08 M Copper (as sulfate orchloride) 0.03 M NaOH 8 g/L Formaldehyde 4 g/L Nickel Sulfate 0.025 g/L2,2′-dipyridyl 0.010 g/L Dithiobiuret or thiomalic acid 0.00005 g/LMethoxy PEG 750 0.075 g/L

Example 4

Concentration Potassium sodium tartrate 0.08 M Copper (as sulfate orchloride) 0.03 M NaOH 8 g/L Formaldehyde 4 g/L Nickel Sulfate 0.025 g/L2,2′-dipyridyl 0.010 g/L Dithiobiuret or thiomalic acid 0.00005 g/L PEG2000 0.100 g/L

Example 5

Concentration Potassium sodium tartrate 0.10 M Copper (as sulfate orchloride) 0.04 M NaOH 10 g/L Formaldehyde 5 g/L Nickel Sulfate 0.050 g/L2,2′-dipyridyl 0.005 g/L Thiomalic acid 0.0005 g/L Methoxy PEG 750 0.075g/L

Example 6

Concentration Potassium sodium tartrate 0.08 M Copper (as sulfate orchloride) 0.03 M NaOH 8 g/L Formaldehyde 4 g/L Nickel Sulfate 0.025 g/L2,2′-dipyridyl 0.010 g/L Dithiobiuret 0.00005 g/L PEG 2000 0.100 g/L

Comparative Example 1

In Comparative Example 1, the electroless copper solution was a standardelectroless copper solution of MacDermid MID 100™ electroless copper(available from MacDermid Enthone, Inc. Waterbury, Conn.)

Comparative Example 2

Concentration Potassium sodium tartrate 0.08 M Copper (as sulfate orchloride) 0.03 M NaOH 8 g/L Formaldehyde 4 giL 2,2′-dipyridy1 0.010 g/LDithiobiuret or thiomalic acid 0.00005 g/L Methoxy PEG 750 0.075 g/L

Comparative Example 3

Concentration Potassium sodium tartrate 0.08 M Copper (as sulfate orchloride) 0.03 M NaOH 8 g/L Formaldehyde 4 g/L 2,2′-dipyridy1 0.010 g/LDithiobiuret 0.00005 g/L PEG 2000 0.100 g/L

As set forth below in Table 1, the improved electroless copper platingbath of the present invention is able to produce a ductile copperdeposit that exhibits a % elongation that is much higher than the %elongation that is achievable with electroless copper plating solutionsof the prior art. Thus, it can be seen that the improved copper platingbath of the instant invention can produce a ductile copper depositexhibiting a % elongation of greater than about 12.0%, greater thanabout 13.0%, greater than about 14.0% and even greater than about 15.0%.This result cannot be achieved with prior art electroless copper platingbaths and certainly cannot provide the improved results in the absenceof EDTA and CN.

TABLE 1 Tape Test % Elongation Tensile strength (psi) Example 1 Pass12.0 44,200 Example 2 Pass 12.0 41,800 Example 3 Pass 15.0 46,100Example 4 Pass 14.0 42,100 Example 5 Pass 15.0 44,600 Example 6 Pass13.5 45,800 Comparative Pass 15 55,800 Example 1 Comparative Pass 4.253,700 Example 2 Comparative Pass 3.2 49,700 Example 3

Finally, it should also be understood that the following claims areintended to cover all of the generic and specific features of theinvention described herein and all statements of the scope of theinvention that as a matter of language might fall there between.

What is claimed is:
 1. An electroless copper deposition composition,comprising: a) a source of copper ions; b) a chelator; c) a source ofalkalinity; d) a reducing agent; e) 0.02 to 0.04 g/L nickel ions; f)0.001-0.05 g/L of a bipyridine; g) 0.00001 to 0.0001 g/L of anadditional stabilizer, wherein the additional stabilizer is selectedfrom the group consisting of dithiobiuret, diethyldithiocarbamate,ammonium, sodium or potassium pyrrolidinethiocarbamate, thiomalic acid,and combinations of one or more of the foregoing; and h) 0.01 to 1 g/Lof a water-soluble polymer; wherein the composition is at leastsubstantially free of ethylenediaminetetraacetic acid, cyanide,ferrocyanide, or cyanide derivatives; and wherein the composition isfree of any additional components that would have a detrimental effecton ductility.
 2. The electroless copper deposition composition accordingto claim 14, wherein the source of copper ions is selected from thegroup consisting of copper chloride, copper sulfate, copper nitrate,copper oxide, and combinations of one or more of the foregoing.
 3. Theelectroless copper deposition composition according to claim 14, whereinthe chelator is selected from the group consisting of tartaric acid andsalts thereof, citric acid and salts thereof, malic acid and saltsthereof, acetic acids and salts thereof, and combinations of one or moreof the foregoing.
 4. The electroless copper deposition compositionaccording to claim 3, wherein the chelator comprises potassium sodiumtartrate.
 5. The electroless copper deposition composition according toclaim 14, wherein the reducing agent comprises formaldehyde.
 6. Theelectroless copper deposition composition according to claim 14, whereinthe bipyridine comprises 2,2′-dipyridyl.
 7. (canceled)
 8. Theelectroless copper deposition composition according to claim 14, whereinthe additional stabilizer comprises dithiobiuret or thiomalic acid. 9.The electroless copper deposition composition according to claim 14,wherein the concentration of the bipyridine in the electroless copperdeposition composition is in the range of about 0.001 to about 0.05 g/L.10. The electroless copper deposition composition according to claim 14,wherein the water soluble polymer comprises a methoxypolyethyleneglycol.
 11. (canceled)
 12. The electroless copper deposition compositionaccording to claim 14, wherein the composition contains no measurableconcentration of ethylenediaminetetraacetic acid, cyanide, ferrocyanideor cyanide derivatives.
 13. The electroless copper depositioncomposition according to claim 14, wherein the molar ratio of chelatorto copper ions is in the range of about 1:1 to about 10:1.
 14. Anelectroless copper plating bath consisting essentially of: a) a sourceof copper ions; b) a chelator; c) a source of alkalinity; d) a reducingagent; e) 0.02 to 0.04 g/L nickel ions; f) a bipyridine; g) 0.00001 to0.0001 g/L of an additional stabilizer, wherein the additionalstabilizer is an organic compound containing divalent sulfur; and h)0.01 to 1 g/L of a water-soluble polymer, wherein the water-solublepolymer is methoxypolyethylene glycol, wherein the electroless copperplating bath is at least substantially free ofethylenediaminetetraacetic acid, cyanide, ferrocyanide or cyanidederivatives.
 15. A method of electroless copper deposition on asubstrate, the method comprising the steps of: contacting the substratewith an electroless copper plating solution for a period of time todeposit copper on the substrate, the electroless copper plating solutioncomprising: a) a source of copper ions; b) a chelator; c) a source ofalkalinity; d) a reducing agent; e) 0.02 to 0.04 g/L nickel ions; f) abipyridine; g) 0.00001 to 0.0001 g/L of an additional stabilizer,wherein the additional stabilizer is an organic compound containingdivalent sulfur; and h) 0.01 to 1 g/L of a water-soluble polymer,wherein the water-soluble polymer is methoxypolyethylene glycol; andwherein the composition is free of any additional components that wouldhave a detrimental effect on ductility.
 16. The method according toclaim 15, wherein the substrate comprises acrylonitrile butadienestyrene.
 17. The method according to claim 16, wherein the substrate isdoped with a copper chromite catalyst and laser ablated, wherein theelectroless copper deposits on the laser ablated substrate.
 18. Themethod according to claim 15, wherein the concentration of thebipyridine in the electroless copper plating solution is in the range ofabout 0.001 to about 0.05 g/L.
 19. The method according to claim 15,wherein the copper deposit exhibits a % elongation of at least 10% asmeasured according to ASTM E-345.
 20. The method according to claim 15,wherein the copper deposit exhibits a % elongation of at least 12% asmeasured according to ASTM E-345.
 21. The method according to claim 15,wherein the copper deposit exhibits a % elongation of at least 14% asmeasured according to ASTM E-345.
 22. The method according to claim 15,wherein the electroless copper plating solution is at leastsubstantially free of ethylenediaminetetraacetic acid, cyanide,ferrocyanide, or cyanide derivatives.
 23. The method according to claim15, wherein the additional stabilizer is present in the electrolesscopper plating solution at a concentration of 0.00001 to 0.0001 g/L,wherein the additional stabilizer is selected from the group consistingof dithiobiuret, diethyldithiocarbamate, ammonium, sodium or potassiumpyrrolidinethiocarbamate, thiomalic acid, and combinations of one ormore of the foregoing.